Rod,
The attached comes from here: http://www.supercontrol.de/cat/ft847faq/ft847faq.htm#s
It is a good general source of info on the FT-847. I have seen some slight variations elsewhere, but it is a good place to start.
73s,
Alan WA4SCA
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Serial Numbers
Updated 10Jan01
Yaesu appears to use the following format for serial numbers on their amateur products:
Year of manufacture-Month of manufacture-Production Run-Individual Unit number, where the month of manufacture is offset by 2, so "C" means January, "D" means February, "E" means March, and so forth.
Example: 8G051234 = 1998, May (fifth month, or "G"), Production Run 05, unit #1234 in this run.
One key serial number range is 8G05. This seems to be the point at which Yaesu had corrected the bi-directional CAT issue and made some other improvements. This version was made in May 1998. Later serial numbers (e.g., 8L09nnnn) all seem to have incorporated the earlier improvements plus new ones.